The purpose of this protocol is to study patients with various neurometabolic disorders. Mucolipidosis type IV (ML-IV), is a developmental and degenerative disease caused by mutations in the MCOLN1 gene leading to an absent or dysfunctional protein called mucolipin. The goal of this protocol is to assess the neurological and medical status of these patients and characterize the clinical and laboratory abnormalities in order to determine the natural history of the disease. Patients will be followed at least yearly with comprehensive clinical, neurological and ophthalmological examinations combined with neuropsychological, blood, urine and radiological tests.